Produced 2006 by US-CERT, a government organization.Updated 2008. 1
Using Wireless Technology Securely
In recent years, wireless networking has become more available, affordable, and easy to use.
Home users are adopting wireless technology in great numbers. On-the-go laptop users often find
free wireless connections in places like coffee shops and airports.
If you’re using wireless technology, or considering making the move to wireless, you should
know about the security threats you may encounter. This paper highlights those threats, and
explains what you need to know to use wireless safely, both in the home and in public. You will
find definitions of underlined terms in the glossary at the end of this paper.
Home Wireless Threats
By now, you should be aware of the need to secure traditional, wired internet connections.*
you’re planning to move to a wireless connection in your home, take a moment to consider what
you’re doing: You’re connecting a device to your DSL or cable modem that broadcasts your
internet connection through the air over a radio signal to your computers. If traditional wired
connections are prey to security problems, think of the security problems that arise when you
open your internet connection to the airwaves. The following sections describe some of the
threats to home wireless networks.
If you fail to secure your wireless network, anyone with a wireless-enabled computer within
range of your wireless access point can hop a free ride on the internet over your wireless
connection. The typical indoor broadcast range of an access point is 150 – 300 feet. Outdoors,
this range may extend as far as 1,000 feet. So, if your neighborhood is closely settled, or if you
live in an apartment or condominium, failure to secure your wireless network could potentially
open your internet connection to a surprising number of users. Doing so invites a number of
• Service violations: You may exceed the number of connections permitted by your
internet service provider.
• Bandwidth shortages: Users piggybacking on your internet connection might use up
your bandwidth and slow your connection.
• Abuse by malicious users: Users piggybacking on your internet connection might
engage in illegal activity that will be traced to you.
For detailed information on securing wired home networks, see “Home Network Security” <http://www.us-
• Monitoring of your activity: Malicious users may be able to monitor your internet
activity and steal passwords and other sensitive information.
• Direct attack on your computer: Malicious users may be able to access files on your
computer, install spyware and other malicious programs, or take control of your
Wardriving is a specific kind of piggybacking. The broadcast range of a wireless access point
can make internet connections possible outside your home, even as far away as your street.
Savvy computer users know this, and some have made a hobby out of driving through cities and
neighborhoods with a wireless-equipped computer—sometimes with a powerful antenna—
searching for unsecured wireless networks. This practice is nicknamed “wardriving.” Wardrivers
often note the location of unsecured wireless networks and publish this information on web sites.
Malicious individuals wardrive to find a connection they can use to perpetrate illegal online
activity using your connection to mask their identities. They may also directly attack your
computer, as noted in the “Piggybacking” section above.
Unauthorized Computer Access
An unsecured wireless network combined with unsecured file sharing can spell disaster. Under
these conditions, a malicious user could access any directories and files you have allowed for
Protecting Home Wireless
While the security problems associated with wireless networking are serious, there are steps you
can take to protect yourself. The following sections describe these steps.
Make Your Wireless Network Invisible
Wireless access points can announce their presence to wireless-enabled computers. This is
referred to as “identifier broadcasting.” In certain situations, identifier broadcasting is desirable.
For instance, an internet cafe would want its customers to easily find its access point, so it would
leave identifier broadcasting enabled.
However, you’re the only one who needs to know you have a wireless network in your home. To
make your network invisible to others, see your access point’s user manual for instructions on
disabling identifier broadcasting. (In Apple wireless networking, this is called “creating a closed
While this kind of “security through obscurity” is never foolproof, it’s a starting point for
securing your wireless network.
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Rename Your Wireless Network
Many wireless access point devices come with a default name. This name is referred to as the
“service set identifier” (SSIS) or “extended service set identifier” (ESSID). The default names
used by various manufacturers are widely known and can be used to gain unauthorized access to
your network. When you rename your network, you should choose a name that won’t be easily
guessed by others.
Encrypt Your Network Traffic
Your wireless access point device should allow you to encrypt traffic passing between the device
and your computers. By encrypting wireless traffic, you are converting it to a code that can only
be understood by computers with the correct key to that code. For more about encryption, see the
US-CERT Cyber Security Tip “Understanding Encryption,” http://www.us-cert.gov/
Change Your Administrator Password
Your wireless access point device likely shipped with a default password. Default passwords for
various manufacturers are widely known and can be used to gain unauthorized access to your
network. Be sure to change your administrator password to one that is long, contains non-
alphanumeric characters (such as #, $, and &), and does not contain personal information (such
as your birth date). If your wireless access point does not have a default password, be sure to
create one and use it to protect your device.
Use File Sharing with Caution
If you don’t need to share directories and files over your network, you should disable file sharing
on your computers. You may want to consider creating a dedicated directory for file sharing,
and move or copy files to that directory for sharing. In addition, you should password protect
anything you share, and use a password that is long, contains non-alphanumeric characters (such
as #, $, and &), and does not contain personal information (such as your birth date). Never open
an entire hard drive for file sharing.
Keep Your Access Point Software Patched and Up to Date
From time to time, the manufacturer of your wireless access point will release updates to the
device software or patches to repair bugs. Be sure to check the manufacturer’s web site regularly
for any updates or patches for your device’s software.
Check Your Internet Provider’s Wireless Security Options
Your internet service provider may provide information about securing your home wireless
network. Check the customer support area of your provider’s web site or contact your provider’s
customer support group.
Produced 2006 by US-CERT, a government organization.Updated 2008. 3
Public Wireless Threats
A wireless-enabled laptop can make you more productive outside your office or home, but it can
also expose you to a number of security threats. The following sections describe some of the
security threats you face when using a public access point.
Evil Twin Attacks
In an evil twin attack, the attacker gathers information about a public access point, then sets up
his or her own system to impersonate the real access point. The attacker will use a broadcast
signal stronger than the one generated by the real access point. Unsuspecting users will connect
using the stronger, bogus signal. Because the victim is connecting to the internet through the
attacker’s system, it’s easy for the attacker to use specialized tools to read any data the victim
sends over the internet. This data may include credit card numbers, username and password
combinations, addresses, and other personal information.
Many public access points are not secured, and the traffic they carry is not encrypted. This can
put your sensitive communications or transactions at risk. Because your connection is being
transmitted “in the clear,” malicious users can use “sniffing” tools to obtain sensitive information
such as passwords, bank account numbers, and credit card numbers.
Many laptop computers, particularly those equipped with 802.11-type WiFi wireless networking
cards, can create ad hoc networks if they are within range of one another. These networks enable
computer-to-computer connections, a situation that creates security concerns you should be
aware of. An attacker with a network card configured for ad hoc mode and using the same
settings as your computer may gain unauthorized access to your sensitive files. You should note
that many PCs ship from the manufacturer with wireless cards set to ad hoc mode by default.
Unauthorized Computer Access
As is the case with unsecured home wireless networks, an unsecured public wireless network
combined with unsecured file sharing can spell disaster. Under these conditions, a malicious user
could access any directories and files you have allowed for sharing.
In public wireless areas, the bad guys don’t even need a computer to steal your sensitive
information. The fact that you may be conducting personal business in a public space is
opportunity enough for them. If close enough, they can simply glance over your shoulder as you
type. Or, they could be peering through binoculars from an apartment window across the street.
By simply watching you, they can steal all kinds of sensitive, personal information.
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Safe Wireless Networking in Public Spaces
Accessing the internet via a public wireless access point involves serious security threats you
should guard against. These threats are compounded by your inability to control the security
setup of the wireless network. What’s more, you’re often in range of numerous wireless-enabled
computers operated by people you don’t know. The following sections describe steps you can
take to protect yourself.
Watch What You Do Online
Because you’re likely to have an unsecured, unencrypted network connection when you use a
public wireless access point, be careful about what you do online—there’s always the chance
that another user on the network could be monitoring your activity. If you can’t connect securely
using a VPN (see “Connect Using a VPN” below), then consider avoiding
• online banking
• online shopping
• sending email
• typing passwords or credit card numbers
Connect Using a VPN
Many companies and organizations have a virtual private network (VPN). VPNs allow
employees to connect securely to their network when away from the office. VPNs encrypt
connections at the sending and receiving ends, and keep out traffic that is not properly encrypted.
If a VPN is available to you, make sure you log onto it any time you need to use a public
wireless access point.
Disable File Sharing
File sharing in public wireless spaces is even more dangerous than it is on your home wireless
network. This is because you and your wireless-enabled laptop are likely to be even closer to
other wireless computers operated by people you don’t know. Also, many public wireless
networks feature peer-to-peer networking in which other computers will attempt to connect
directly to yours. To leave file shares open in this kind of environment is to invite risk. To
prevent attackers from gaining access to your sensitive files, you should disable file sharing
when connecting to a public wireless access point. Consult the help file for your operating
system to learn how to disable file sharing.
Be Aware of Your Surroundings
When using a public wireless access point, you should be aware of what’s going on around you.
Are others using their computers in close proximity to you? Can others view your screen? Are
you sitting near a window through which someone, using binoculars, could get a view of your
screen? If any of these conditions exist, your sensitive data might be at risk. Consider whether it
Produced 2006 by US-CERT, a government organization.Updated 2008. 5
is essential to connect to the internet. If an internet connection is not essential, disable wireless
networking altogether. If you do need to connect, use caution and follow the steps noted above.
The following sections provide a quick summary of the steps you should take to secure your
home wireless network and to use wireless technology safely in public spaces.
Home Wireless Security
When you use a wireless router or access point to create a home network, you trade wired
connectivity for connectivity delivered via a radio signal. Unless you secure this signal, strangers
can piggyback on your internet connection or, worse, monitor your online activity or access files
on your hard drive. By taking the following actions, you can help secure your wireless home
network against these threats.
• Change the default system ID of your wireless access point or router.
• Change the default password for your system.
• Turn off identifier broadcasting.
• Encrypt wireless communications. (WPA-based encryption offers better protection than
• Use your router’s built-in firewall to restrict access to your network.
• Keep your wireless system patched and up to date.
Public Wireless Security
Accessing a wireless connection from a coffee shop or airport terminal may be convenient and
even fun, but you should note that public access points (frequently called hot spots) are often
insecure. The following are some steps you should consider taking before connecting to a public
• Use a virtual private network (VPN) if possible.
• Avoid using passwords and providing personal information to web sites.
• Encrypt your files.
• Be aware of your surroundings.
References and Further Reading
Articles and Web Sites
Bowman, Barb. “WPA Wireless Security for Home Networks,” Microsoft,
Produced 2006 by US-CERT, a government organization.Updated 2008. 6
Brain, Marshall. “How WiFi Works,” How Stuff Works,
Collins, Hilton. “Critical Steps for Securing Wireless Networks and Devices.” Government
Tecnology, < http://www.govtech.com/gt/406582> (2008).
Dolcourt, Jessica. “How to secure your wireless network.” cnet Australia,
Lee, Wei-Meng. “Securing AirPort Extreme Networks with WPA,” O’Reilly Network,
Lee, Wei-Meng. “Setting Up an 802.11b Home Wireless Network,” O’Reilly Network
McDowell, Mindi. “Understanding Encryption” (US-CERT Cyber Security Tip ST04-019), US-
CERT, <http://www.us-cert.gov/ cas/tips/ST04-019.html> (2004).
Vamosi, Robert. “Beware your evil twin (hot spot, that is),” CNET,
“Wireless Life,” CNN.com <http://www.cnn.com/SPECIALS/2004/wireless/> (2004).
Gast, Matthew. 802.11 Wireless Networks: The Definitive Guide, Second Edition. Sebastapol,
CA: O’Reilly & Associates, Inc., 2005
Potter, Bruce and Fleck, Bob. 802.11 Security. Sebastopol, CA: O’Reilly & Associates, Inc,
Negrino, Tom and Smith, Dori. Mac OS X Unwired. Sebastopol, CA: O’Reilly & Associates,
Ross, John. The Book of Wireless: A Painless Guide to Wi-Fi and Broadband Wireless, Second
Edition. San Francisco, CA: No Starch Press. 2008.
Weeks, Roger et al. Linux Unwired. Sebastopol, CA: O’Reilly & Associates, Inc, 2002.
Produced 2006 by US-CERT, a government organization.Updated 2008. 7
802.11 802.11 is a specification for wireless local area networks (WLANs)
developed by the Institute of Electrical and Electronics Engineers
(IEEE). There are several 802.11 specifications. These specifications
describe how a wireless-enabled computer or device communicates
with a base station or wireless access point and with other wireless-
enabled computers or devices. The current 802.11 specification is
Access point In a wireless local area network (WLAN), an access point is a station
that transmits and receives data. An access point connects users to
other users within the network and can also connect the WLAN to a
Ad hoc network A local area network in which computers and network devices are in
close proximity to others on the network. These devices are connected
temporarily or for specific purposes.
DSL DSL stands for digital subscriber line. This is a dedicated, high-
bandwidth telecommunications line provided by a telecommunications
or telephone company. DSL lines are capable of providing high-speed
internet access, but are only available to subscribers who live within a
designated distance of a telephone company central office.
Encryption In internet technology, encryption is the transformation or encoding of
information into a form that can only be understood by someone who
has the correct “key” for decoding it. It is an important tool for
securing network traffic.
Hotspot A hotspot is a wireless network node that provides an internet
connection. More and more hotspots are becoming available in public
locations such as airports, coffee shops, and hotels.
Piggyback Piggybacking refers to illicitly accessing the internet through an
unsecured wireless network.
Router A router is a device that processes traffic entering and exiting a
network. It examines individual bits of network traffic, known as
packets, and determines where to send the packet. Routers can attach
to computers on a network (or other routers) using cables. Wireless
routers perform the same job as wired routers, only they convert
network traffic to a radio signal. Routers in a home network are most
often connected to a broadband cable or DSL modem.
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VPN VPN stands for virtual private network. VPNs are a secure way to use
the internet as an extension of a private network. They use encryption
and a special internet protocol to create a “tunnel” through the internet
from one point to another. This traffic cannot be accessed by those
unable to connect to the VPN. Businesses frequently use VPNs to
secure private network traffic moving between two geographically
distinct offices, or between remote employees using laptops and the
WEP WEP stands for wired equivalent privacy, a security protocol designed
to provide a wireless network with a level of security and privacy
comparable to that of a wired LAN. In WEP, data moving between
computers and access points is encrypted.
Wi-Fi Wi-Fi is short for wireless fidelity. The term applies to wireless
networks that employ 802.11-type security. An organization called the
Wi-Fi Alliance coined the term. This organization tests wireless
products work together and certifies those that pass as "Wi-Fi
certified" (a registered trademark).
WPA WPA stands for Wi-Fi protected access. Like WEP, WPA is a security
protocol designed to provide a wireless network with security and
privacy. WPA provides stronger data encryption and better user
authentication than WEP.
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